Measuring and testing – With fluid pressure
Reexamination Certificate
2000-03-20
2002-02-26
Larkin, Daniel S. (Department: 2856)
Measuring and testing
With fluid pressure
C073S15000R, C073S037500
Reexamination Certificate
active
06349588
ABSTRACT:
This application relates to an inexpensive, accurate, and efficient system and method for performing bulge testing of films, coatings, and/or layers. More particularly, this invention relates to improved systems and methods for performing bulge testing of such films, coatings, and/or layers, including improved methods of manufacture, improved membranes for use in such testing, improved methods for manufacturing membranes, improved testing components, improved testing procedures, and improved materials for use with same. Systems and methods herein enable the determination of elastic properties, inelastic properties, time-dependent properties, residual stresses, and the like by measuring the bulging of a membrane and/or film when one side thereof experiences an increase or decrease in pressure. In certain alternative embodiments, bulging caused by inherent pre-stress (without application of pressure or evacuation) in the film is measured to determine the aforesaid properties.
CLAIM TO COPYRIGHT IN REFERENCE TO APPENDIX
An appendix portion of the disclosure of this patent application contains material which is subject to copyright protection (see FIGS.
15
-
70
). 37 C.F.R. §1.96(a) (1). The copyright owner has no objection to the reproduction by anyone of the patent document as it appears in the Patent and Trademark Office files or records, but otherwise reserves all copyrights whatsoever. Instructions for software for carrying out some of the methods and systems, has been filed with the United States Patent and Trademark Office herewith as
FIGS. 15-70
.
BACKGROUND OF THE INVENTION
It is known that properties of a film, coating, or layer of a given material differ from those of the same material in bulk form. For example, thin films have different yield stresses, creep behavior, and elastic properties than do bulk forms of the same material. The only way to determine the qualities or properties of thin films is to measure the films themselves.
As technology advances, many elements including storage media (e.g. disks), integrated circuits, cutting tools, sensor arrays, wear surfaces, LCD matrix arrays, and the like include films, coatings, and/or layers deposited on a substrate. The term “film” as used herein is to encompass films, coatings, and layers of varying thicknesses. Typically, each film (e.g. thin film) has different residual stress characteristics and different thermal and/or mechanical properties, which may affect the performance, reliability, or durability of devices including such films. The ability to determine mechanical properties and residual stress characteristics of thin films is thus desired. Bulge testing is one way in which to do this.
In prior art bulge testing systems, as shown in
FIG. 1
, circular or rectangular film
1
having a thickness “t” is clamped over cavity or orifice
3
in mounting structure
5
, and pressure is applied to the bottom side of film
1
from within the orifice. The out-of-plane deflection or bulging of film
1
is measured as a function of the applied pressure enabling determination of a pressure-deflection curve and the residual stress in the film. Prior art
FIG. 2
shows the vertical equilibrium of film
1
when pressure is applied via cavity
3
.
The stress state of film
1
is two dimensional so that properties in the plane of film
1
are measured through the use of known equations which include as parameter(s) the geometry of the film, the properties of the material composing the film, the differential pressure applied across the film, the center deflection of the film, and in-plane residual stress. For example, see “Mechanical Properties of Thin Films” by Nix, found in the 1988 Institute of Metals Lecture, Volume 20A, November 1989; “Measuring the Mechanical Properties of Thin Metal Films by Means of Bulge Testing of Micromachined Windows” by Paviot, et. al., Mat. Res. Soc. Symp. Proc. Vol. 356, 1995 Materials Research Society; “Mechanical Behavior of Thin Films” by Vinci and Vlassak, Annu. Rev. Mater. Sci. 1996-26:431-62; “The In-Situ Measurement of Mechanical Properties of Multi-Layer Coating” by Lin, 1990 MIT Dept. of Mat. Sci. & Eng., Archives; “Load Deflection Analysis for Determining Mechanical Properties of Thin Films With Tensile and Compressive Residual Stresses” by Bulsara, 1995 MIT Dept. Mat'l. Sci. & Eng.; and “New Experimental Techniques and Analysis Methods for the Study of the Mech. Prop. of Materials in Small Volumes”, Chapt. 3, by Vlassak (1994), the disclosures of which are all hereby incorporated herein by reference.
Bulge testing of circular or square freestanding windows of different geometries of film
1
mounted to structure
5
allows one to determine the biaxial modulus of the film as well as the residual stress in the film. Knowledge of these characteristics is important in determining durability and other mechanical and structural characteristics of the film.
With regard to square films or membranes, for example, the elastic deflection as a result of a uniform pressure “p” applied in the cavity is known to be approximately described by the following equation (see Paviot, et. al. referenced above):
p
=
c
1
(
v
)
Et
(
1
-
v
)
a
4
w
0
3
+
c
2
σ
res
t
a
2
w
0
where c
1
(v) is about 1/(0.792+0.085 v)
3
and c
2
equals about 3.393. In this expression, w
0
is the deflection of the center of the film or membrane, “t” is the film or membrane thickness, and “a” is the width of the membrane. Utilizing the above-identified equation enables one to determine the biaxial modulus Y=E/(1−v) and the residual stress in the film.
As disclosed in Vinci and Vlassak (cited above), the pressure-deflection relationship for a thin circular film or membrane with a residual stress in a bulge test is approximated by the equation:
P
=
(
1
-
0.241
v
)
(
8
3
)
(
E
1
-
v
)
(
t
a
4
)
w
0
3
+
4
(
σ
0
t
a
2
)
w
0
in the elastic regime, where w
0
is the deflection of the center of the film or membrane, “P” is the applied pressure, “t” is the film or membrane thickness, and “a” is the film or membrane radius. Using this equation enables one to determine the biaxial modulus E/(1−v) and the residual stress in the film.
It is noted that other equations, which are disclosed and explained in the above-identified publications, may be used to determine residual stress and/or elastic modulus of films subjected to bulge testing.
It is also known to test composite membranes including two or more layers. For example, see pages 90+ in Chapter 3 of Vlassak, “New Experimental Techniques and Analysis Methods for the Study of the Mechanical Properties of Materials in Small Volumes” (1994), where bulge testing of a composite membrane including two or more layers is discussed. As discussed by Vlassak, silicon oxide or silicon nitride films can be used as substrates or membranes onto which metal films are deposited. This technique can be applied to a variety of films without major changes to the sample preparation method.
Still referring to Chapter 3 of Vlassak, pages 90+, it is known that the residual stress in, and elastic properties of, the silicon nitride or silicon oxide membrane by itself can be determined by bulge testing the membrane without a film overlayer. Thereafter, when a metal overlayer film is deposited onto the silicon oxide or silicon nitride membrane, its biaxial modulus can be calculated from-the biaxial modulus of the composite film. If Poisson's ratio of the metal film is known, Young's modulus of the metal film can be calculated from the biaxial or plane-strain modulus. The residual stress in the metal film is calculated via the average residual stress in the composite, as the weighted average of the stresses in the membrane and the metal film overlayer.
As discussed in section 3.4 of Vlassak, Chapter 3, it is known to fabricate freestanding silicon nitride films on silicon substrates by way of micromachining. Such silicon nitride membranes are then used as substrates or membranes for ot
Brown Stuart B.
Correia Paulo Jorge Furtado
Lynch Kevin R.
Mlcak Richard
Muhlstein Christopher L.
Exponent Inc.
Larkin Daniel S.
Liniak Berenato Longacre & White
Wiggins David J.
LandOfFree
System and method for performing bulge testing of films,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System and method for performing bulge testing of films,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System and method for performing bulge testing of films,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2966345